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Goldberg Eaglet 50 Conversion
From: Robert Van Housen vanhelsing@directlink.net
Hi Ken,
I was trying to click on the link to your Eaglet 50 electric, but the link was too old.
Could you email me some pictures and specs when you have the time? I was flying mine last year with an old Veco .19 baffled
when she crashed, and I'd like to rebuild it so I can get more flying in locally. I'm new to electrics, but have built a few
successful glow kits. Could you tell me exactly what changes you made other than building the fuse all balsa (sans plywood)?
Follow up:
Date: 3/12/03 12:52:36 AM Eastern Standard Time
Thanks for the fast reply Ken,
It's not critical that it be a true park flyer. That picture on the link looks great!
(members.aol.com/kmyersefo/myplanes.htm KM) Nice
color scheme. I tried to set mine up as a tail dragger last year, but couldn't work out a reliable tail gear setup. What did you use
for that?
I just used a fixed tailwheel. Electrons are precious, therefore I don’t taxi
out. I set the plane on the runway and do a straight takeoff. I fly until the power is too low to fly or the BEC (Battery
Eliminator Circuit of the Electronic Speed Control) kicks in. Then I land, with no taxi back.
Also, when you converted to the balsa fuse, did you use solid sheeting on the sides
and bottom (I probably need to look at the picture again) or did you cut sections in the balsa to lose more weight?
I used 1/16" balsa sheet. There is little advantage to
"holing". You could just use cross-braces on the top and bottom, and that would be a good idea for the
"Park Flyer" recommendation below.
I'm going to leave the sections for the windshield and windows solid for structural
strength, because I had the wing tear off the front dowel rod in a crash last year. I also found the stabilizer to be ridiculously
fragile, so I increased some of the dimensions there for rigidity and increased the elevator size by 150%. I'm looking at getting
the Great Planes S-600 GD ESC system with gear drive from Tower Hobbies (62.89). Is that a good choice? Like I said I'm
new to electrics.
That’s a good idea about the windshield area. I had no problems with the
stock tail. The power system you’ve mentioned is probably not the best choice in this plane. I’m going to attach my
unpublished notes on the Eaglet 50 conversion to this email, so that you can see my thinking about this plane, back in
1998 when I was constructing it. I’m also sending, via attachment, several more Ampeers with info on the Eaglet 50
conversion. You’ll also find some info at this link:
www.geocities.com/CapeCanaveral/Launchpad/5767/mommar98.html
Be sure to read the "Getting Started In Electric Powered Radio Controlled Flying" in the January 2003
Ampeer: members.aol.com/kmyersefo/ampjan03.PDF
I don’t know whether you used ailerons on your original plane, but I found
them ineffective with this model, therefore I’d recommend just going rudder-elevator-motor (REM).
With all the information I’ve sent to you, you’ll see my thinking evolving on
powering this plane. The following are my latest thoughts.
Park Flyer:
Goldberg Eaglet 50 Wing Area: 432 sq.in.
Target Flying weight not to exceed: 45 oz.
Wing Loading: 15 oz. sq.ft.
Motor: Graupner Speed 480 Race 7.2v #6330, Kv=3212 Io=2 Rm=0.129, 3.7 oz, $22 -
www.hobby-lobby.com/speed280.htm or other sources
Reducer: MJ8104 4.1:1 Gearbox for 480, ball bearing, $ 22.40 -
www.hobby-lobby.com/gear480.htm or other sources
Prop: APC 11x5.5E, $2.85 -
www.azarr.com/propsandadaptors.htm
Cells: 9 Sanyo CP-1300SCR, $3.75 ea., 1.23 oz. -
www.rc-aero.com/biz/bandt/#nicads, or a
9-cell pack from Diversity Model Aircraft $58.00, 12 oz. approx. -
www.flydma.com/batteries/index.html
ESC (electronic speed control) w/BEC Astro Flight 215D, $49.95, 0.32 oz. -
www.newcreations-rc.com or JE350 Jeti 35 Microprocessor Controller, $ 59.90, 0.88 oz. -
www.hobby-lobby.com/jeti.htm
Receiver: FMA Extreme 5 Sub Micro Receiver, $44.95 + $10.95 crystal, 0.4 oz. -
www.fmadirect.com or Hitec Micro 555, $58.99 + $10.99
crystal, 0.75 oz. - www.towerhobbies.com
Servos: (2 rud. - elev.) Hitec HS-81 Standard Micro Servo, $17.99 ea., 0.58 oz. -
www.towerhobbies.com
Onboard Radio System weight w/ESC, lightest = 1.88 oz. heaviest = 2.79 oz.
Power System weight w/prop est. 17 oz.
Target flying weight: 45 oz. or less
Estimated Static Amp Draw: 16 amp
Estimated RPM with APC 11x5.5E prop: 6,200
Estimated Flying Speed: low 30-MPH range
Orme’s Rule: 8 - 12 cells
Ken’s Modified Orme’s Rule: 8 - 14 cells
Flight Factor: 1.99
Diameter Factor w/ 11x5.5E: 2.17
Pitch Factor w/ 11x5.5E: 0.50
"Speed" to RPM Factor w/ 11x5.5E: 2.44
Motor efficiency: 70%
System efficiency: 63%
Estimated flight time: 8-10 minutes with decent throttle management.
Easy Sport/Trainer:
Goldberg Eaglet 50 Wing Area: 432 sq.in.
Target Flying weight not to exceed: 52.2 oz.
Wing Loading: 17.4 oz. sq.ft.
Motor: Graupner Speed 500 Race 7.2v #1789, Kv=2850 Io=2 Rm=0.075, 5.8 oz, $16.11 -
www.newcreations-rc.com or other sources
Reducer: HLH712 Olympus Belt Drive 2.22:1, $ 27.30, 2 oz. -
www.hobby-lobby.com/drives.htm or other sources
Prop: APC 10x5E, $2.60 -
www.azarr.com/propsandadaptors.htm
Cells: 8 Sanyo CP-1700SCR, $4.00 ea., 1.62 oz. -
www.rc-aero.com/biz/bandt/#nicads, or
an 8-cell pack from Diversity Model Aircraft $55.00, 13 oz. approx. -
www.flydma.com/batteries/index.html
ESC (electronic speed control) w/BEC Astro Flight 215D, $49.95, 0.32 oz. -
www.newcreations-rc.com or JE350 Jeti 35
Microprocessor Controller, $ 59.90, 0.88 oz. -
www.hobby-lobby.com/jeti.htm
Receiver: FMA Extreme 5 Sub Micro Receiver, $44.95 + $10.95 crystal, 0.4 oz. -
www.fmadirect.com or Hitec Micro 555, $58.99 + $10.99
crystal, 0.75 oz. - www.towerhobbies.com
Servos: (2 rud. - elev.) Hitec HS-225BB High Performance Mini Servo, $23.99 ea., 0.95 oz.
- www.towerhobbies.com
Onboard Radio System weight w/ESC, lightest = 2.62 oz. heaviest = 3.53 oz.
Power System weight w/prop est. 22 oz.
Target flying weight: 52.2 oz. or less
Estimated Static Amp Draw: 26 amp
Estimated RPM with APC 10x5E prop: 8,200
Estimated Flying Speed: low 40-MPH range
Orme’s Rule: 8 - 12 cells
Ken’s Modified Orme’s Rule: 8 - 14 cells
Flight Factor: 2.3
Diameter Factor w/ 10x5E: 1.37
Pitch Factor w/ 10x5E: 0.50
"Speed" to RPM Factor w/ 10x5E: 2.7
Motor efficiency: 71%
System efficiency: 60%
Estimated flight time: 6-8 minutes with decent throttle management.
Sport/Sport Scale
Goldberg Eaglet 50 Wing Area: 432 sq.in.
Target Flying weight not to exceed: 61.2 oz.
Wing Loading: 20.4 oz. sq.ft.
Motor: Kyosho Magnetic Mayhem 22x1 Motor, Kv=2660 Io=2 Rm=0.090, 6.9 oz, $19.99 -
www.towerhobbies.com
Reducer: Modelair-tech H-750 MK I 2.4:1, $ 53.95, 3 oz. -
www.modelairtech.com/belt.html
Prop: APC 10x7E, $2.60 -
Cells: 9 Sanyo CP-2400SCR, $4.50 ea., 2.11 oz. -
www.rc-aero.com/biz/bandt/#nicads, or a
9-cell pack from Diversity Model Aircraft $74.00, 19 oz. approx. -
www.flydma.com/batteries/index.html
ESC (electronic speed control) w/BEC Astro Flight 215D, $49.95, 0.32 oz. -
www.newcreations-rc.com or JE350 Jeti 35
Microprocessor Controller, $ 59.90, 0.88 oz. -
www.hobby-lobby.com/jeti.htm
Receiver: FMA Extreme 5 Sub Micro Receiver, $44.95 + $10.95 crystal, 0.4 oz. -
www.fmadirect.com or Hitec Micro 555, $58.99 + $10.99 crystal, 0.75 oz. -
www.towerhobbies.com
Servos: (2 rud. - elev.) Hitec HS-225BB High Performance Mini Servo, $23.99 ea., 0.95 oz. -
www.towerhobbies.com
Onboard Radio System weight w/ESC, lightest = 2.62 oz. heaviest = 3.53 oz.
Power System weight w/prop est. 30 oz.
Target flying weight: 61.2 oz. or less
Estimated Static Amp Draw: 27 amp
Estimated RPM with APC 10x7E prop: 7,500
Estimated Flying Speed: low to mid-50 MPH range
Orme’s Rule: 8 - 12 cells
Ken’s Modified Orme’s Rule: 8 - 14 cells
Flight Factor: 2.7
Diameter Factor w/ 10x7E: 1.37
Pitch Factor w/ 10x7E: 0.70
"Speed" to RPM Factor w/ 10x7E: 3.25
Motor efficiency: 71%
System efficiency: 59%
Estimated flight time: 8-10 minutes with decent throttle management.
After providing Robert with the above information, I received
the following:
Hi Ken,
That's a ton of great information. Sorry, I took so long
responding, but have been working on getting my first glider airborne. Looking at your stats,
I think I will build the Park Flyer version. Can you recommend a book or combination of books
for building/converting to electric. Seems like quite a bit of math and I think I should have
some reference books for future projects. I'll let you know how the building progresses.
Thanks again,
Robert
Sorry, I can’t recommend any books on conversions. Last month
I gave several links that will certainly get you started.
One of the biggest problems with conversions, is defining
the task. In the example of the Eaglet 50, I’ve designed three conversions based on the three
tasks. I don’t believe that there can ever be a really good "conversion" book,
because electric motors don’t have a glow equivalent, no matter how much we want them to. There
are some general rules, but with e-power, for any given motor, you can just increase the power
out until destruction of the motor or other electronics of the power system.
Keep reading the Ampeer, the Ezone Magazine, eflight list,
the threads of the eflight news group and check the plane ratings on the EFO site for good
ideas about powering e-planes and conversions from glow power.
For those who may have forgotten, or never seen, my Eaglet
50 conversion, I’ve provided an old photo.
Suppliers Mentioned:
B&T R/C Products: www.rc-aero.com/biz/bandt
Diversity Model Aircraft: www.flydma.com
E Cubed R/C /Azarr: www.azarr.com
Ezone Magazine: www.ezonemag.com
FMA Direct: www.fmadirect.com
Hobby Lobby: www.hobby-lobby.com
Modelair-Tech: www.modelairtech.com
New Creations R/C: www.newcreations-rc.com
Tower Hobbies: www.towerhobbies.com
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Formula for CG Location
From: Lowrie McLarty jmclarty@wi.rr.com
Milwaukee, WI
Enclosed is a CG formula for finding the best location for batteries and servos relative
to the motor and each other.
Having the CG, (center of gravity), where it should be for safe flying, is an age old
problem for aircraft designers. The CG position is especially difficult to predict for electrics because the motor and battery and
servos are such a high percentage of the total model weight that their relative location determines the CG position. Shifting
components to other positions after the model is built may not be a happy experience. Designers of aircraft, and those upgrading
to a greater weight motor and battery capacity, have a need to know the location options for all weighty items.
The formula shown can include other items such as landing gear or camera. If the
desired position of the CG is known, then an item, such as a servo or battery that can be moved, should have its weight placed in
the formula and the distance from Ref. to this weight can be calculated.
(Thanks Lowrie. Yes, there is a Walled Lake, MI. It located just a little
north and east of Wixom, MI. Wixom is just off I-96, where the Lincolns and T-birds are made. KM)
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Goldberg Jr. Falcon
From: Pat Harvey patharvey@charter.net
Hi Ken:
We swapped e-mails in January regarding the Jr. Falcon. I went ahead with the
project, sort of.
I did build the wing with a fiberglass spar and a fiberglass leading edge much like
the X-250. The airfoil is the original Jr. Falcon except it has 1 1/4 inch ailerons added (8 1/2 inch total chord). There is no
dihedral and no washout. It’s a pure flat wing. The Hitec HS-81 servo is in the underside of the wing. This version has a 42 inch
wingspan with approximately 357 square inches of wing area.
The fuselage is balsa, much like a Simple 400 except it has a "domed"
construction forward of the wing such that the wing actually nestles into the fuselage from the rear. The wing is held on with
rubber bands. All incidences are 0 - 0 - 0.
The stab and elevator are slab balsa with holes for weight reduction but the same
outline as the original. The elevator is driven by another HS-81 servo mounted below the trailing edge of the wing, but in the
fuselage.
The vertical fin / rudder is fixed. The outline is similar to a Falcon 56 with slab
construction and holes for weight reduction.
Covering is a semi-transparent iron-on from Hobby Lobby.
Power is from a Rocket 400 geared 3:1 driving a 9x6 prop. The speed control is a
Pixie 20P. The pack is an 8-cell 800 mAh Nicad. In level flight it pulls about 6 amps. At static full throttle it pulls 14.4 amps at
6,500 RPM.
It flies well with strong vertical and easy wide loops, much like MotoCalc suggested.
I just thought I'd let you know.
Thanks,
Pat
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Sig Somethin’ Extra Plane Rating
From: Dave Thacker DAVTHACKER@aol.com
Plane Rating: ****
Greetings,
Last winter I obtained (can't take credit for building) a nice Sig Somethin’ Extra with
Astro Flight 40G swinging a Master Airscrew 13-8 prop on 20 CP-2400SCR cells. The all up weight (AUW) was 7 lbs.
The original owner reported 6 minute flights, fun but no unlimited vertical. This
looked like an excellent electric subject.
I applied some ElectriCalc salve to the project and converted it thusly. ElectriCalc
did in fact verify no unlimited vertical on original setup.
I changed the pack over to a much lighter 1700AUP NiMH 24 cell pack. I changed
the prop to 12-10. This gets the amps to about 34 at around 750-800 watts. This is OK on the 1700AUP for short periods (note,
limit is about 30 amps normally on this cell). I discarded the museum 4.8V AA Rx pack and replaced with a U-Bec. I replaced
the Astro Flight ESC with a new Orbit ESC and replaced Hitec 555 with a FMA M5. Servos were HS-85MG and I left them. I
then replaced the standard wheels with Robbe light weight wheels.
The re-outfitted ship now weighs 6 lbs. The front 60 seconds or so has unlimited
vertical. Ecalc says about 3 minutes at full throttle time, but this is a fun-fly model so actual flying times proved to be much
longer. Flight times average 8 minutes as I like to fly. I've calculated my average flight current at 11.45 amps.
I like models that I can fly close in and low and this model fills the bill. I enjoy every
minute flying this machine. Comments from my wet friends are "looks as good as a glow".
This kit looks to be built 100% stock. I weighed the bird, less all electronics it’s
3 lbs. In my view, if it were built with thinner ribs, lighter tail (rear of fuse is light but feathers are heavy as stock), replaced the
ply with balsa, used a lighter more modern power plant and paid general close attention to electric detail it might be lowered to a
2 lb. airframe with a 5 lb. flying weight.
I'd like to build one thusly, just to see, but time is short always for me. Other options
for this model would be maxing out the Astro 25G on 18 to 20 1900FAUP and a 12-8 prop giving a lighter weight machine
(maybe just under 5 lb.) with similar output power. Of course there are brushless options as well.
If you've been thinking of doing this conversion, get on the ball, you'll have a
"ball" with the Somethin' Extra.
Happy Flying!
Dave Thacker, radicalrc.com
RADICAL RC - The best in R/C electronics. Servos, Receivers, Wiring, Harnesses, Switches, Wire, Sanyo Packs NiCad
and NiMH.
Thanks Dave. Here are the numbers that I ran on Dave’s Somethin’ Extra.
Wing Area: 614 sq.in. (mfg.)
Weight: 96 oz. - 6 lb.
Wing Loading: 22.5 oz./sq.ft.
Wing Span: 51.5 in. (mfg.)
Astro Flight 40
Wt. 13.5 oz.
Kv = 682, Io = 2.0, Rm = 0.121
1.68:1 reducer: Wt. 1.5 oz.
Total Motor + reducer Wt. = 15 oz.
24 1700AUP (1.27 oz.) = 30.5 oz.
Motor + reducer % of total = 15.6%
Cell weight % of total = 31.8%
Total motor + reducer + 1700AUP battery = 47.4%
Note the following mathematical estimations are based on the voltage near the beginning of the pack discharge and apply to static testing conditions. Amp draw will decrease in the air and as the pack discharges through the flight, but since most of us tach and test on the ground, these figures can be used for comparison.
Using 12x10 prop:
Watts in 960 (32*1.25*24) - Watt/lb. 160
Watts to motor 767.7 - Watt/lb. 128
Watts to prop 603.6 - Watt/lb. 100.6
RPM 8,200
Orme’s Rule: 12 - 18 cells
Ken’s Modified Orme’s Rule: 12 - 21 cells
Flight Factor: 2.649
Diameter Factor w/ 12x10: 1.18
Pitch Factor w/ 12x10: 0.83
"Speed" to RPM Factor w/ 12x10: 4.67
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The Hastings NZ E-rally
From: Nick Furmage maxsea@paradise.net.nz
One of the really nice things about the Internet is that it lets us share our
hobby with interested folks around the World. Nick sent along the following that I wanted to share with you.
Hi Ken,
I just attended this e-rally a couple weeks ago. We all had great fun before the rain
came (Bugger)! This one was in Hastings on New Zealand’s North Island. The East coast usually has very nice weather, but
not this day. Here is a link to some of the photos.
www.acehobby.co.nz/ossb2/club/hbrf/new_page_1.htm
The other link is to the North Shore E-rally in New Zealand’s biggest city,
Auckland, which is in the top of the North Island.
www.acehobby.co.nz/ossb2/club/nsmac/club/Electricday2003.htm
I hope they are of interest. Electric is growing quite fast down here, and we have
all the whiz bang gear like everyone else.
Cheers, Nick Furmage
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Keeping Small Gunther Props On
From: Ray Williams rwilliams@campac.net.au
Hi Ken,
Like most modelers who use Gunther props, I have had them depart the aircraft at
the most inconvenient times.
My first solution was a drop of cyno and slip it on. This worked for some time but,
eventually the glue let go with the same results.
Whilst at the bench one day, I had a thought that it could be a small pocket of air in
the spinner between the tip of the motor shaft and the pointy end of the spinner that expands with the heat of the shaft and pops
the prop.
I used a pin and forced a small hole through the spinner. I placed a drop glue on
the shaft and pushed the prop on and a small amount of glue dripped out of the hole.
This particular aircraft is a small v-tail aerobatic called a "Yorkee". It
has been modified to take a modified 480 motor and runs on 8 cells. The motor pulls 10 amps and turns over at 14,900 rpm. The
prop has now been on for approximately 8 months and had not departed once.
I have been toying with the aerial photo bit and have been reading about the
problems. You may find a better picture will be produce if you take the pictures on the glide as even electric motors have a bit of
vibration. My first effort is to place a one shot camera on the front of a big 2.3 m glider.
Keep Flying,
Ray Williams
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Serious error in May 2003 Li-Po article
In my part of the article, right near the beginning of the second paragraph, I stated,
"When cells are put in series, the total amp draw can be safely increased." THIS IS NOT TRUE! I either mistyped
or had a mental lapse when I wrote it, as the rest of the paragraph is about paralleling the cells. It should have read, "When
cells are put in parallel, the to total amp draw can be safely increased." I’ve actually changed and
reposted the May 2003 Ampeer in all formats online. If you have already downloaded it, please get the corrected version at
http://members.aol.com/kmyersefo
If you have already read it, please note that I meant paralleling allows for an
increased amp draw, NOT putting Li-Po cells into series. I apologize for any confusion this may have caused.
If you receive the Ampeer via the mail, a new May 2003 page 3/4 has been
included with this issue. Please replace the original.
Thank you Robert Comerford for reading so carefully and letting me know of this
very important error.
Ken Myers
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Aeronaut F-7-F Tigercat
from: From: Dan Parsons dapars@comcast.net
Hi, Ken,
It's been a while since I've sent you any info on planes or activities here in
Albuquerque. My latest is the Aeronaut F-7-F Tigercat ARC that I have been flying for the last several weeks, and I now have
around 18 flights on it. This is one that is really worth writing home about!
I've been flying scale planes since the late fifties and twins since 1960 and this
Tigercat, aside from my deHavilland Hornet twin, is the best I have ever flown. As a matter of fact, it flies exactly like my 80 in.
OS-61 powered Hornet and has no vices that I have discovered. It does everything well, from catapulting to all the way through
the flight to landing on grass on it's nacelles. It lands equally well at just above stall to high speed touchdowns. Speaking of
catapulting, with all the cat shots off Navy carriers on TV these days, I'm well calibrated and the Tiger is right on the money.
This is a fine "kit" with everything first class from the fiberglass fuselage and
nacelles to the built-up and sheeted wing. Although an ARC, there is a fair bit of work to do, but boy, is it worth it!
I made a few changes (as usual) by simplifying several procedures, reducing the
ailerons to scale size, reducing the dihedral to improve flight characteristics (and looks, in my opinion) and filling in the sheeting of
the open bay on the wing and the unsheeted horizontal stab so I could glass them.
Here are the specs:
1---- W.S.--52.3 in.; Area--2.96 sq.ft.
2----Wt--86 ozs.
3----Wing loading--29ozs./sq.ft.
4----Motors--Jeti Phasors 15/4 brushless in parallel
5----Controllers--Jeti Jes 30-P
6----Servos--Elev & Rud-Dymond 200/35 in.ozs. Aileron- Cirrus CS 10BB/12 in. ozs., one for each aileron.
7----Props----Aeronaut white fiberglass 8.5 X 6"
8----Propulsion----10 cells Sanyo 2600 NiMH
9----Receiver & servo battery pk.--- 4 cells Sanyo 350 mAh
10----CG for first flight at 28% of the MAC then moved to 30% after the 5th flight. Plans at 33%
Final notes: The power/prop combination at full power (45A on bench
test ) provides both high speed and excellent climb, just like the full scale version. Flight at half throttle is smooth and still fast and
even has some climb left. Speaking of speed, at full power it can quickly reach distances where it becomes hard to see so one
needs to be a bit careful! Since the props I'm using provide exactly the kind of flying I like ("spirited"), I have not tried any other
prop. The scale ailerons are quite a bit smaller than the plans show and work very well, though I had to increase the plan throws
(not surprising). The stall is quite gentle; ( I love the Clark Y airfoil). So far, my aerobatics consist of huge loops, slow rolls,
4-point rolls, reverse Cuban eights, inverted flight, stall turns and a couple I don't remember. The Tiger does them all beautifully
and with authority. This is one outstanding flying machine!! When I get the new Li-Poly battery, that will provide 15 minute
flights instead of 5-6 min and it will be 6 oz. Lighter. I will have the perfect plane. If anyone is interested in doing this Tigercat,
give me a phone call, and I'll be happy to help and give you further info. (505) 296-2353.
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Avro in Australia
From: Benny Laird lairds@iprimus.com.au
I'm just getting into electrics. I started with Tom Hunt’s Lowwatt and now have
Peter Rakes N28 built as well as his Avro504. Both are unflown as yet. Thanks for all your info, I have it printed up for easy
reference.
I'm having a go at designing a Vickers Vimy for twin 400 with gearbox's. Started
at 48 in. span but I’m thinking this may be too big?
Anyway here's a picture of the Avro.
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NIRAC
(NATIONAL INDOOR REMOTE-CONTROLLED AIRCRAFT COUNCIL)
COMPETITION NOTICE
FIRST ANNUAL INDOOR R/C CHAMPIONSHIP
DATES: Saturday May 31, 2003
And Sunday, June 1, 2003
Location: Oakland Yard, Waterford, Michigan
(approx. 100 miles north of Toledo, northwest of Detroit and just east of the Pontiac
International Airport)
Facility Size: 240 X 300 feet, with an 82 feet ceiling
Contest Director: Dave Robelen @ aplusfarm@hovac.com
Events: 6 events planned, with trophies to third place
An overall high point Championship Award
Individual Event rules and a registration form can be found on the NIRAC website:
www.nirac.org
Hobby Vendors will be selling on-site
Information on local lodging and a Saturday night banquet can be
obtained from John Worth @ johnworth@cox.net
General information available from NIRAC President
Bob Wilder @ rjwmaw5@attbi.com
And NIRAC Vice President
Bob Aberle @ baberle@optonline.net
Pre-Registration is recommended!
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Arial Photos & a Gear Ratio?
From: David Summers ironsidz@look.ca
Ken:
Against all your advice, I have purchased a GWS Slow Stick and I am into digital
aerial photography using the Mustek GSmart Mini 3 as per:
webhome.idirect.com/%7eironsidz/airfoto.htm
I have attached one of my shots - greatly compressed for rapid transmission.
Believe it or not, with a 6 cell 7.2 volt 600 mAh battery, 2 servos, ESC, motor, gear
box, propeller and camera the All-Up-Weight is 1.5 pounds.
The CMOS cameras, such as the Aiptek and Mustek, cannot stand any vibration
while writing the image to memory. Because they do not write to a buffer, any vibration results in wavy lines in the image. The
trick is get to altitude, turn off the motor, trim for glide and snap a series of photos.
The only complaint I have about the Slow Stick is the rate of climb. These CMOS
cameras are better at altitude as motion at lower levels gives some funny results. In looking for better performance. I have been
looking at the data on the GWS EPS 370 motor/gearbox/propeller combinations. I have searched your site for the answer to my
riddle and am still confused.
Situation:
The GWS chart shows a 4.4 to 1 gear ratio and an 8x4.3 propeller as an Excellent
match. Equally it shows a 13.0 to 1 gear ratio and a 14x7 propeller as Excellent.
In total, there are 7 combinations that are rated as Excellent. I have just given the
two extremes.
Questions:
Q1. If I want to maximize hauling power to get to altitude, while minimizing forward speed, which gearbox and propeller
combination is better?
Q2. Which combination is better for endurance?
Q3. In general terms, what is the relationship between gear ratios and propeller diameter/pitch?
David Summers
webhome.idirect.com/~ironsidz
Answers:
On a given motor, with the same battery pack, the larger the gear ratio the larger
the prop diameter will be to pull the same current. The output power, at the same current on the same battery with the same
motor does not change. Remember that all props are different and it is very hard to compare one prop to another, but for the
sake of this example I’ll say the 8x4.3 and 14x7 behave in the same manner. I’ll say the 8x4.3 is turning at 6,000 RPM. (This
number is made up and not from any actual testing - just a number to use.) PowerOut = 8/124*4.3/12*63*1.31
= 20 watts out. For the 14x7 (20 watts out/(14/124*7/12*1.31))1/3 = 2.417 KRPM or 2,417 RPM.
The 14x7 has more static thrust, but no more output power, just more
"pull". The relative speed, and I mean relative, since the Slow Stick is not clean by any means, is 4.3*6 = 25.8 mph
for the 8x4.3 and 2.417*7 = 16.9 mph for the 14x7. This should answer your questions 1 and 3. There is no difference in
endurance at the same amp draw except, unless you keep the prop from wind-milling, the larger prop will cause more drag,
therefore less endurance. The more amps you draw, the less motor endurance/motor run time you have.
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